Patterned vertically aligned liquid crystal display

ABSTRACT

In a vertically aligned mode LCD, a gate line and a storage line are formed on a substrate in parallel, and a storage electrode and a cover pattern are formed as branches of the storage line. The storage electrode is overlapped with an aperture of a common electrode formed on an upper substrate. The cover pattern is located between a pixel electrode and a data line to prevent a light leakage. Accordingly, an alignment error margin of the upper substrate and the lower substrate is increased, an aperture ratio is enhanced, and repairing the high pixel defect is possible. Further, the light leakage caused by a voltage of the data line is prevented.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 10/430,412,filed May 7, 2003, which is a continuation of application Ser. No.09/417,076, filed Oct. 13, 1999 now U.S. Pat. No. 6,577,366.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a liquid crystal display having a wideviewing angle, and more particularly, to a liquid crystal display ofwhich viewing angle is made wide by patterning apertures in electrodes.

(b) Description of the Related Art

Liquid crystal displays (LCDs) typically include two substrates and aliquid crystal layer interposed between the substrates. Thetransmittance of light is controlled by the intensity of an electricfield applied to the liquid crystal layer.

In a vertically aligned (VA) mode LCD, liquid crystal molecules take ona homeotropic orientation in which long axes of the molecules areperpendicular to the substrate. This configuration cuts off lightsalmost completely in an “off” state where an electric field above acertain value is not applied to the liquid crystal layer. In thenormally black mode, since brightness in the off state is extremely low,a significantly higher contrast ratio can be obtained when compared tothe conventional twisted nematic LCDs. However, in an “on” state, inwhich an electric field above a certain value is applied between theelectrodes, a tilt direction of the liquid crystal molecules isirregular such that a direction of the long axes of some liquid crystalmolecules becomes identical to a polarizing direction of either an upperor a lower polarizer film. When this occurs, the liquid crystalmolecules are unable to rotate the polarizing direction of light,thereby blocking the light with the polarizer films. These parts of theLCD appear black, degrading the picture quality. To solve this problem,many methods of patterning electrodes are proposed. In U.S. Pat. No.5,136,407, a method of forming line-shaped apertures on electrodes ofone of the two substrates is disclosed. In U.S. Pat. No. 5,309,264,there is disclosed a method of forming “X”-shaped apertures ontransparent electrodes of one of the two substrates.

In order to maintain a storage capacitance, either storage lines or gatelines are used. In the latter case, an aperture formed at a pixel abovea gate may form an electric field between the gate line and a commonelectrode and leak lights by moving the liquid crystal material, when avoltage is applied to the gate line. This limits the design of theapertures of the electrodes. Accordingly, it is hard to design anelectrode pattern that allows a bigger margin for pixel alignment.Further, in a ring gate structure, it frequently causes a high pixeldefect, which leaves pixels continuously in a white state as a result ofshorting the pixel electrodes with the data lines or the gate lines.This problem is difficult to repair. Finally, an aperture ratio is lowsince light can not be transmitted in the areas where the gate lines areformed.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to solve the aboveproblems.

It is an object of the present invention to provide an electrode patterndesign which enables a bigger margin for pixel alignment.

It is another object of the present invention to provide a method forrepairing high pixel defects.

It is yet another object of the present invention to increase anaperture ratio.

A liquid crystal display according to the present invention includes afirst gate line formed on a lower substrate, a first storage line formedon the lower substrate, a data line formed on the lower substratecrossing and insulated from the first gate line and the firstindependent line, a pixel electrode formed on the lower substratecrossing and insulated from the first storage line, and a commonelectrode formed on an upper substrate with an aperture dividing thepixel electrode into a plurality of sections. The outer boundary of thepixel electrode is rugged and the aperture formed on the commonelectrode has various shapes depending on the aspects of the presentinvention.

The storage line may have storage electrodes and/or cover patterns toincrease a storage capacitance.

The cover patterns may overlap the adjacent pixel electrodes or datalines. Or they may just follow the boundaries of the pixel electrodesand data lines to keep a uniform distance between them.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and other advantages of the present invention willbecome apparent from the following description in conjunction with theattached drawings, in which:

FIGS. 1A and 1B are partial layout views respectively of a lower paneland an aperture formed on an upper panel of a liquid crystal display(LCD) according to a first embodiment of the present invention;

FIG. 1C is a partial plan view of an LCD according to the firstembodiment of the present invention; and

FIGS. 2 to 9 are partial plan views of LCDs according respectively tosecond to ninth embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. In the drawings, the thickness of layersand regions are exaggerated for clarity. Like numbers refer to likeelements throughout. It will be understood that when an element such asa layer, region or substrate is referred to as being “on” anotherelement, it can be directly on the other element or intervening elementsmay also be present. In contrast, when an element is referred to asbeing “directly on” another element, there are no intervening elementspresent.

FIGS. 1A, 1B and 1C are partial layout views respectively of a lowersubstrate of a liquid crystal display (LCD), an aperture formed on anupper substrate of an LCD, and the two substrates in an assembled stateaccording to a first embodiment of the present invention. It is to beassumed that elements appearing in the drawings are provided over anentire surface of the substrates, and not just once or twice as shown inthe drawings.

As shown in FIG. 1A, gate lines 11 and a storage line 12 extend in onedirection on the lower substrate. A storage electrode 121 is formedperpendicular to the gate lines 11 and the storage line 12, the storageelectrode 121 being branched from the storage line 12. The storageelectrode 121 has projections 124 that are formed outwardly from thestorage electrode 121 in a direction opposite to a longitudinal axis ofthe storage electrode 121. Adjacent projections 124 are formed at auniform distance from each other. Although the storage line 12 comes tohave the same potential as that of common electrodes, which are formedon the upper substrate, the storage line 12 may also have a differentpotential. Further, when enough storage capacitance is made by thestorage line 12, the storage electrode 121 need not be formed. It ispreferable that the gate lines 11, the storage line 12 and the storageelectrode 121 are formed simultaneously by a single photolithographyprocess on the lower substrate.

Data lines 13, which are insulated from the gate lines 11 and thestorage line 12, are formed perpendicular to the gate lines 11 and thestorage line 12. A plurality of pixel electrodes 14, which are insulatedfrom the storage electrode 121, is formed in a pixel area defined by thegate lines 11 and the data lines 13 (i.e., each pair of gate lines 11and data lines 13 forms a pixel area). The pixel electrodes 14 aresubstantially square with rounded corners The longitudinal axis of thestorage electrode 121 passes through the center of the pixel electrodes14, and the projections 124 of the storage electrode 121 are located atthe center of the square-shaped pixel electrodes 14. The pixelelectrodes 14 may be made of ITO (indium tin oxide) fortransmitting-type LCDs, and made of aluminum (Al) for reflection-typeLCDs.

Redundant gate lines 18 are formed on the gate lines 11 and between thedata lines 13. The redundant gate lines 18 are used to repair gate lines11 in the event the gate lines 11 become disconnected. If one of thegate lines 11 becomes disconnected, the two severed ends are shortedwith the corresponding redundant gate line 18 using a laser. Theredundant gate lines 18 may be provided in the LCD after its two endsare pre-connected to the gate lines 11. The redundant gate line 18 maybe formed on the same layer and of the same material as either the datalines 13 or the pixel electrodes 14.

FIG. 1B shows an aperture 15 that is formed on a common electrode of theupper substrate. The aperture 15 includes a plurality of shapes 16 thatextends outward on both sides of the aperture 15 in a direction oppositeto a longitudinal axis of the aperture 15. The shapes 16 extend apredetermined distance and become increasingly narrow toward ends of theshapes 16 to form a point at the ends of the shapes 16. The aperture 15is formed in such a manner to make boundaries of the aperture 15 smoothsince such smooth boundaries make an arrangement of liquid crystalmolecules more uniform and have the liquid crystal molecules responsequicker. This is also why the pixel electrodes 14 are formed withrounded edges. Accordingly, whatever shape the pixel electrodes 14 andaperture 15 may take, it is preferable that the boundaries of theaperture 15 and the pixel electrodes 14 be a straight line, or a curvewith an obtuse angle.

FIG. 1C shows the upper substrate and the lower substrate when they areassembled. When assembled, the storage line 12 overlaps a longitudinalaxis of one of the shapes 16 of the aperture 15. The remaining shapes 16overlap the projections 124 of the storage electrode 121 such that acenter of the shapes 16 corresponds to a center of the projections 124.As a result, the substantially square shape of the pixel electrodes 14is divided into four sections. At this time, it is preferable that outeredges of the pixel electrodes 14 and areas of the pixel electrodes 14outlined by the aperture 15 make a closed loop, thereby forming aplurality of sections in each pixel electrode 14. Also, it is preferablethat long axes of the liquid crystal molecules in one section of thepixel electrodes 14 defined by the shapes 16 of the aperture 15 arearranged at a 90° angle (on average) to long axes of the liquid crystalmolecules in an adjacent section of the pixel electrodes 14. If thepixel electrode 14 is formed as a perfect square, and the polarizingfilms are perpendicularly arranged, the long axes of the liquid crystalmolecules in each of the sections of the pixel electrodes 14 arearranged at a 45° angle against the polarities of the polarizing filmswhen viewed from above. Accordingly, a wide viewing angle may beobtained.

As described above, since the storage electrode 121 is connected to thestorage line 12, a common voltage may be applied to the storageelectrode 121. Accordingly, no electric field is formed between thestorage electrode 121 and the common electrode. Therefore, no lightsleak even when apertures are formed above the storage electrode 121.

Further, since there is no gate ring, restrictions in forming aperturepatterns are significantly reduced. Therefore, as described above, it ispossible to form the aperture 15 having a plurality of shapes 16 on thecommon electrode of the upper substrate, and the plurality of connectedpixel electrodes 14 having a substantially square shape with its edgesrounded. As a result, an error margin in a photolithography process toform the aperture 15 is increased. Furthermore, the boundaries of thesections of the pixel electrodes 14 formed as a closed loop reduce theuneven textures, in which the liquid crystal molecules are arrangedunevenly, in each of the sections of the pixel electrodes 14. Inaddition, since the aperture 15 may be formed large enough to leave somelength after fully dividing the pixel electrodes 14 into the sections,even if the lower and upper substrates are somewhat misaligned whenassembling, the boundaries of the sections of the pixel electrodesnevertheless form a closed loop. In other words, a bigger alignmenterror margin can be obtained.

Also, the storage electrode 121 formed where the aperture 15 overlaps,which normally appears black as a result of the weak electric field,minimizes a reduction in the aperture ratio to maintain storagecapacitance.

Finally, a high pixel defect may be converted into a low pixel defect,which is less problematic than the high pixel defect, by shorting thepixel electrode 14 causing the problem to the storage line 12 by a lasermelting process. Next, the shorted portions between the pixel electrode14 and the gate line 11 or the data line 13 are cut using the lasermelting process.

FIG. 2 is a partial plan view of an LCD according to a second embodimentof the present invention.

In the second embodiment, the first cover pattern 122 and the secondcover pattern 123, which are connected to the storage line 12, areadditionally provided. These cover patterns are preferably made of thesame material and at the same time as the gate lines and the storagelines. The first cover pattern 122 and the second cover pattern 123preferably are provided partially covering the pixel electrodes 14 andthe data lines 13 in an identical direction with the data lines 13. Thefirst cover pattern 122 and the second cover pattern 123 ends beforecontacting the gate lines 11. The first cover pattern 122 and the secondcover pattern 123 overlap with a part of the data lines 13 to increase acapacitance formed between the cover patterns 122 and 123 and the datalines 13.

The cover patterns 122 and 123 decrease the electric field between thedata lines 13 and the common electrode to prevent the liquid crystalmolecules from reacting to the electric field between the data lines 13and the common electrode. Furthermore, the cover patterns 122 and 123act as a black matrix and minimize the leakage of light. Also, the coverpatterns 122 and 123 increase storage capacitance.

FIG. 3 is a partial plan view of an LCD according to a third embodimentof the present invention.

The third embodiment is the same as the second embodiment except thatthe storage electrode 121 is removed.

When the storage line 12 and the cover patterns 122 and 123 can obtainenough storage capacitance, the aperture ratio is increased by notforming the storage electrode 121.

FIG. 4 is a partial plan view of an LCD according to a fourth embodimentof the present invention. The fourth embodiment is the same as thesecond embodiment except that the cover patterns 122 and 123 do notoverlap any part of the pixel electrodes 14.

This can eliminate large variances in storage capacitance even if amisalignment occurs between a photo shot for forming the cover patterns122 and 123 and a photo shot for forming the pixel electrodes 14.Accordingly, stitch defects are prevented.

FIG. 5 is a partial plan view of an LCD according to a fifth embodimentof the present invention.

The fifth embodiment is the same as the fourth embodiment except thatboundaries of the cover patterns 122 and 123 are curved to roughlycorrespond to the curves in the boundaries of the pixel electrodes 14.Accordingly, a uniform distance is maintained between the cover patterns122 and 123 and the pixel electrodes 14.

This makes the electric field formed between the cover patterns 122 and123 and the pixel electrodes 14 uniform. Therefore, this uniformelectric field affects the electric field formed between the pixelelectrodes 14 and common electrodes, symmetrically in all the sectionsof the pixel electrodes 14 defined by the aperture 15.

FIG. 6 is a partial plan view of an LCD according to a sixth embodimentof the present invention.

The sixth embodiment is the same as the first embodiment except that asecond storage line 16 is additionally formed on the storage electrode121. The second storage line 16 is formed in place of one of theprojections 124 and is parallel with the first storage line 12. Thesecond storage line 16 is formed on the same layer as the first storageline 16. The number of storage lines 12 and 16 may be further increased.The second storage line 16 is provided as a fail-safe. That is, thisconfiguration enables the LCD to be driven even if one of the twostorage lines 12 and 16 is disconnected.

FIG. 7 is a partial plan view of an LCD according to a seventhembodiment of the present invention.

A first gate line 71 and a second gate line 76 are formed on thesubstrate, and a connector 77 connects the two gate lines 71 and 76. Itis preferable that the second gate line 76 overlaps the aperture 15,which is formed in the common electrode of the upper substrates suchthat the aperture ratio is not reduced. A storage line 72 that overlapsthe aperture 15 is formed in parallel with the gate lines 71 and 76.Other elements of the LCD are identical in structure with those of thefirst embodiment shown in FIG. 1C.

The storage capacitance is obtained by the second gate line 76 and thestorage line 72 is provided to repair the high pixel defect.

FIG. 8 is a partial plan view of an LCD according to an eighthembodiment of the present invention.

In the eighth embodiment, there is a pixel electrode 84 having a firstaperture 841. The first aperture 841 is formed in the shape of connectedcrosses (+) which are aligned in a line and having widths that narrow ina direction away from a center of each cross. A common electrode has asecond aperture 85 formed in the shape of a square ring, sides of whichare cut at its center and which are narrowed in a direction toward thecenter of the sides. The remaining elements are identical in structurewith those described in the first embodiment, and the first coverpattern 122 and the second cover pattern 123 are the same as those ofthe fourth embodiment.

The storage electrode 121 is formed to overlap the first aperture 841that originally appears as a black area. Accordingly, the aperture rationeed not be reduced to form a storage capacitance. The cover patterns122 and 123 decrease the electric field between the data lines 13 andthe common electrode to prevent liquid crystal molecules from reactingto the electric field between the data lines 13 and the commonelectrode. Furthermore, the cover patterns 122 and 123 act as a blackmatrix and minimize the light leakage. Also, the cover patterns 122 and123 increase storage capacitance. At this time, a second storage line(not shown) connected to the first storage line 12 through the storageelectrode 121 may be additionally formed on the same layer as, and inparallel with, the first storage line 12. Further, the first aperture841 and the second aperture 85 may be formed in other shapes.

FIG. 9 is a partial plan view of an LCD according to a ninth embodimentof the present invention.

The gate line 11, the data line 13 and the redundant gate line 18 areidentical in structure with those of the first embodiment. However,aperture patterns of the pixel electrode 94 and the common electrode aredifferent from the first embodiment, and the shape of a storage line 92is also different from the storage line 12 of the first embodiment.

A first bottom aperture 951 and a second bottom aperture 952 extendingthrough the pixel electrode 94 obliquely from a left boundary toapproximately a right boundary of the pixel electrode are formedsymmetrically with regard to the center of the pixel electrode. A thirdbottom aperture 96 extends into the pixel electrode 94 horizontally apredetermined distance from the right boundary. The distance between thefirst bottom aperture 951 and the second bottom aperture 952progressively increases in a direction from the left boundary to theright boundary. A storage line 92 is formed on the same layer as thegate line 11 and overlaps the pixel electrode 94. The independent line92 is not straight but rather angled and has a branch 921.

A first top aperture 97 and a second top aperture 98 extending obliquelyand symmetrically to each other, and a third top aperture 99 angled at amid point are formed on the common electrode. The third top aperture 99is equidistant from the first and second top apertures 97 and 98. Thefirst top aperture 97 and the second top aperture 98 respectively havevertical branch apertures 971 and 981 extended in a vertical direction(FIG. 9). The third top aperture 99 has two vertical branch apertures991 extending in the vertical direction at both ends, and a horizontalbranch aperture 992 protruding in the horizontal direction at the midpoint. At this time, the vertical branch apertures 971, 981, and 991overlap boundaries of the pixel electrode 94.

When assembled, the pixel electrode aperture pattern 951, 952 and 96 andthe common electrode aperture pattern 97, 98, 99, 971, 981, 991 and 992are alternately arranged. The storage line 92 overlaps the third topaperture 99, and the branch 921 also overlaps the third top aperture 99.

As described above, an LCD according to the present invention increasesthe alignment error margin of the upper and lower substrates and theaperture ratio. Also, the high pixel defect can be repaired, and thelight leakage problem caused by the data line voltage is prevented.

In the drawings and specification, typical preferred embodiments of thepresent invention have been disclosed. Although specific terms areemployed, they are used in a generic and descriptive sense only and notfor purposes of limitation, the scope of the invention being set forthin the following claims.

1. A liquid crystal display, comprising: a gate line formed on a lowersubstrate; a storage line formed on the lower substrate; a data lineformed on the lower substrate crossing and insulated from the gate lineand the storage line; a pixel electrode formed on the lower substratecrossing and insulated from the storage line, the pixel electrode havinga first aperture pattern; a common electrode formed on an uppersubstrate and having a second aperture pattern; and a storage electrodeconnected to the storage line, wherein the storage line, storageelectrode, first aperture pattern, and second aperture pattern eachcomprises a straight portion slanting to the gate line, and wherein along axis of a liquid crystal molecule is arranged perpendicular to asubstrate when an electric field is not applied.
 2. The liquid crystaldisplay of claim 1, wherein the storage electrode overlaps the secondaperture pattern.
 3. The liquid crystal display of claim 2, wherein thestorage electrode slants to the gate line.
 4. The liquid crystal displayof claim 1, wherein the first aperture pattern comprises: a first andsecond aperture extending through the pixel electrode obliquely from aleft boundary to approximately a right boundary of the pixel electrode,the first and second apertures formed symmetrically with respect to acenter of the pixel electrode; and a third aperture extending into thepixel electrode horizontally a predetermined distance from the rightboundary.
 5. The liquid crystal display of claim 4, wherein the firstaperture pattern and the second aperture pattern are arrangedalternately.
 6. The liquid crystal display of claim 5, wherein thesecond aperture pattern comprises: a first and second aperture extendingobliquely and symmetrically to each other; and a third aperture angledat a mid point and formed on the common electrode; wherein the thirdaperture of the common electrode is equidistant from the first andsecond apertures of the common electrode.